Patent GB-228751-A (GB)
Title: Improvements in telephone systems
IPC: H04Q3/00
Filed: 1924-04-22
Abstract: 228,751. Relay Automatic Telephone Co., Ltd., and Ward, F. M. April 22, 1924. Automatic exchange systems.-In a small private exchange, particularly for business premises, in which a calling subscriber, Fig. 1, and a called subscriber, Fig. 5, are directly connected over an idle talking trunk ABF, Fig. 2, the wanted line is selected by a " marker," Fig. 3, controlled by a series of marking-wires, shown at the bottom of Figs. 1, 3 and 5, which extend in common to each of the sub-stations and are selected in various combinations by means of keyboards. For example, in the detailed description given in the succeeding paragraphs, the subscriber BNS, Fig. 1, wishing to call subscriber RS, Fig. 5, depresses his keys R, S. The system shown also comprises means for interrupting an existing connection to establish a more urgent call, for giving " con. ference " facilities, for calling an operator to establish external calls,. and for calling a subscriber absent from his telephone. Establishment of local connection. The removal of the calling subscriber's receiver and the depression of keys R, S, complete circuits 2, 2<1>; 2, 2<11>, in which relays LE, R, S3 energize. Relay LE completes circuit 4 in which relay LM4, individual to the first idle trunk, energizes, operates similar relay LM4<1> in other groups (if, as in the present case, the subscriber's lines are grouped) and energizes relay TC4 which connects the calling line to the seized trunk. Relay LM4 also completes circuits for relays BB, RG. Relay TC4 locks up in circuit 8 in series with the cut-off relay CO which completes circuit 9 for feed relav A. Relay G energizes to mark the selected trunk busy. The operation of relay LM4<1> completes the marking circuit 3 prepared by relays R, S3, this circuit including relays TC8, IOC' which complete the connection of the wanted line to the trunk ABF, and lock up in circuit 7, including the called cut-off relay CO<1>. Ringing. Relay RG remains locked up over circuit 10 in series with a trembler bell which operates by shunting its own coil. When the called subscriber replies, circuit 10 is broken and relay RG releases and connects up feed relay B. Relay BB also releases. Supply of microphone current. The circuits 9, 11 of the feed relays A, B include resistances w, x respectively. Called line busy. In this case, circuit 3 is open at contacts of relay CO<1> so that circuit 10 is not completed, relay RG is released as soon as relay CO operates, and relay BB remains locked up and transmits busy tone over circuit 12. Urgent call. The subscriber BNS after getting the busy signal hangs up and may then establish an urgent call to the busy subscriber by pressing bis key P in addition to keys RS, and again removing his receiver from its hook. In this case, relay PC is operated over circuit 13 to open circuit 4 and to complete circuit 14 for relay CF which connects the calling line to a special line c, f. The wanted line RS also is connected to this line c, f, by the operation of relay CF<1> in circuit 15. The operation of CF<1> also breaks down the existing connection. If any third subscriber attempts to call either of the parties connected over the line c, f, circuit 10 will be open at the contacts of relay CF<1> and the busy tone will be given as before. Conference facilities. A number of subscribers by simultaneously pressing their keys O and lifting their receivers complete circuit 16 for relay 0 which in turn completes circuit 17 for relay PC. Circuits 14 are then completed and the subscribers are connected to the special line c, f, by the operation of their relays CF, CF<1>, &c. Calling an operator. The depression of key B energizes relay B and completes circuit 19 for relay MX. Signal OA energizing over circuit 20 locks over circuit 20a, until the operator plugs into jack JA. Calling a subscriber absent from his telephone. The depression of a key C in accordance with a prearranged code may operate a number of bells, hooters &c., connected in series with a battery to the wire to which the keys C are connected.